System for desolventizing solventextracted solid organic particles



Oct. 19, 1954 B. KARNOFSKY LVENTIZING SOLVENT ORGANIC PARTICLES ed June 27, 1950 -EXTRACTED INVENTOR GEORGE B. KARNoFsKY Patented Oct. 19, 1954 ascissa SYSTEM FOR DESOLVENTIZING SOLVENT- EXTRACTED SOLID ORGANIC PARTICLES George B. Karnoisky, Oakmont, Pa., assigner, by mesne assignments, to Biaw-Knox Company, Pittsburgh,y Pa., a corporation of Delaware Application June 27, 1950, Serial No. 170,631

17 Claims.

ticles at a temperature generally below the solvent boiling point without requiring` resort to vacuum conditions or the use of low-boiling solvents. This system employs a gaseous evaporating medium including some solvent vapor and a relatively inert gas and produces a solventfree solids product without substantially changing the moisture content of the particles. Preferably, the system of this invention is conducted at atmospheric pressure and recycles such gaseous evaporating medium of controlled composition respectively in both the usual desolventizer vessel and deodorizer vessel passages.

In the conventional practice of stripping solvent from solid organic particles, such as soybean akes or the like, immediately following the extraction step, it was usual to pass such particles through horizontal cylindrical vessels generally denominated the desolventizer and deodorizer respectively. Such vessels usually were steam jacketed and contained rotating paddles helically arranged to move the particles through the vessels. Upon discharge from the desolventizer, such particles passed into the deodorizer and upon leaving the deodorizer were toasted, nished and stored. Although no steam was customarily admitted into the desolventizer vessel, steam was used within the deodorizer vessel and iniiuenced both the evaporation of solvent and the iinal moisture content of the particles discharged from the deodorizer vessel.

The use of steam jacketing in the conventional practice and of steam within the deodorizer involved the risk of the overheating of the solid particles being desolventized. Overheating may produce objectionable denaturation of the proteins in the particles. In United States patent application Serial No. 737,915, filed March 28, 1947, in the name of Eugene H. Leslie, now U. S. Patent No. 2,571,143, a system is disclosed in which gaseous medium including an inert gas may be recycled through a heater and unjacketed desolventizer vessel of novel construction to evaporate solvent from the solid particles passing through such vessel.

In the system of this invention whether usinto and maintained in equilibrium. Further, relatively sensitive control of the respective composition and physical conditions can be provided and maintained in the vapor circuits for each of the said steps. In this way, a temperature rise of the solvent-extracted solid organic particles undergoing desolventizing in the desolventizer and deodorizer vessels may, if desired, be prevented and, actually, the temperature may be reduced in the passage ci the particles through the two vessels.

Moreover, the temperature rise of such particles in the desolventizer vessel where the overwhelming preponderance of solvent recovery is usually effected, may be held within a very narrow range and below the boiling point, under normal pressure conditions, of the solvent being evaporated and recovered. In addition, the solvent dew-point of the gaseous fluid within the desolventizer vessel and within the deodcrizer vessel may be respectively controlled to insurer against any material condensation of solvent upon the particles passing through said vessels. Still further, in the system of this invention the sensible heat of such particles passing through the deodorizer vessel may bev utilized to evaporate such solvent remaining in such particles. The deodorizing is in principal effect a nal step to reduce the percentage of solvent in the particles undergoing processing substantially to zero.

Other objects and advantages of this invention will be apparent from the following description and from the drawing, which is schematic only, showing a preferred layout embodying the system of this invention.

In the operation of the system of this invention solvent-extracted solid organic particles such as soybean iiakes are fed to a desolventizer vessel l through an inlet H in which a conventional screw conveyor I2 operates. Anl outtake dome I3 surmcunts inlet H and freely communicates with the interior or vessel lil. A helical blade I4 is mounted on longitudinal bars i5 which in turn are fastened at their respective ends to end plates it. End plates llt are suitably journaled in the desolventizer for rotation and movement of blade I4 in such a manner as to advance such solid organic particles from the end oi vessel IB adjacent inlet Il to an outlet il' at the other end thereof. Longitudinal Scrapers I8 are also alixed to bars i5 and assist in cascading said particles through the internal space within vessel I during the progress of such particles toward outlet I7. Suitable means (not shown) are provided for turning end plates it and the associated rotating members within vessel it).

A mixture of gaseous fluid enters vessel l0 through a vapor inlet i9 which is preferably located intermediate the ends of vessel I0. This gaseous fluid also preferably comprises a controlled proportion of recirculated solvent vapor and an incombustible and unieactive gas, such as carbon dioxide or nitrogen, which is inert rel-- ative to any of the materials present. in the desolventizing system. In some cases air may be used as the gas in the solvent evaporating gaseous fluid passed through vessel Il), as, for eX- ample, when desolventizlng particles which were extracted with noninammable solvents. Usually accompanying such mixtures of gas and solvent vapor will be a proportion of water vapor dependent upon the known circumstances responsible for the presence of such water vapor such as the percentage of water in said particles and others. The function of the gaseous fluid atmosphere in the desolventizer is to provide heat to vaporlze solvent in the particles using the partial pressure of the incondensable gas in the gaseous fluid sothat evaporation occures below the boil-ing point temperature of the solvent.

Gaseous fluid entering inlet. lill divides and passes through the interior of vessel I in contact with the moving and cascading particles, toward dome I3 and auxiliary dome 2D'. The gaseous iluid exiting through dome I3 flows countercurrent to the movement of the solids in vessel Ill while that gaseous fluid exiting through dome 2li flows cocurrent to the movement of said particles. Gaseous iiuid leaving both domes I3 and is augmented by the solvent and water evaporated from said particles during the passage thereof through vessel I0.

The gaseous vapors exiting through dome 2G pass through a vapor line 2I and a second vapor line 22 which leads into the intake of a blower 23. An orice 24 is positioned in pipe 2| to regulate the volume of gaseous iiuid exiting through dome 20I relative to the volume of gaseous fluid exiting through dome I3 in accordance with the requirements` of a particular operation conducted under the system of this invention.

Gaseous fluid exiting through dome I3 including the solvent and water vapor evaporated from said particles passes through a vapor line 25 into a condenser 26 where solvent and water vapor is condensed substantially in the amount evaporated from the particles during the passage thereof through the entire vessel i0'. Cooling water enters the space between tube sheets 2l through an inlet 23. and leaves the condenser through an outlet 28. A conventional tem-perature controller regulates the volume of now of such cooling water to maintain a predetermined vapor temperature in the vapor outlet 3i of condenser 26. The gaseous fluid which is not condensed in condenser 2B flows through outlet 3|, at which point it is saturated, and into a vapor line 32 at the temperature preset by controller 30.

A. surge reservoir vessel 33 is filled with the component gas, such as carbon dioxide, used in the gaseous fluid atmosphere passed through vessel I'IJ. This gas is kept preferably at prevailing atmospheric pressure by being vented through a vent pipe 34 connected to a conventional vent condenser 35 for thev plant. Reservoir 33 isl connected by a pipe 36 to line 32 thereby determining the pressure in the recycled vapor circuit leading to blower 23 and supplying whatever additional incondensable gas is required for makeup purposes. A pressure tank 3I containing such gas is arranged to continuously bleed the proper CII amount of gas into line 36 through the predetermined setting of a valve 38 in conjunction with a new meter 39 positioned in connecting line 40 opening into line 35. This proper amount of such gas will include that amount required for make-up in the gaseous atmosphere circuits of the system of this invention plus the amount required to exclude air from passing through vapor line 34 into surge tank 33. It is to be noted that pipe 36 is connected to recirculating pipe 32 intermediate the outlet of condenser 26 and a vapor heater 4I, thereby regulating the pressure of the gaseous fluid atmosphere circuits and the admission of make-up gas by such connection along that portion of the circuit which has the lowest temperature.

The vent line 314 stabilizes operations under the system of this invention by allowing the. escape of additional gaseous iluid Whenever the pressure in the gaseous fluid circuits tends to arise above atmospheric. Further, whenv the pressure in those fluid circuits tends to fm1. below the. preselected uniform temperature,` atmospheric in. this case, make-up gas. passes. through pipe 36- into the circuits to maintain them at atmospheric pressure.. This pressure is. substantially atmospheric throughputr the entire gaseous fluid circuits inasmuch asv the blowers, passages, orifice 2li, heater and. condensers are. constructed to provide. the desired circulation of the fluid with minor pressure diilerenti'als across the several circuits of the system.

In the case of the use of inert gases, such as nitrogen, which are lighter than air, the vent pipe 34 should be connected to the bottom ot reservoir vessel 33y and the pipe 33 should be connected to the top outlet of vessel 33. This is a matter that will be readily understood by those familiar with the bleeding of gasesv intov systems, In cases i-n which air may be used as the unreactive gas relative to the other materials in the system, no surgey vessel 33 nor` apparatus 3-1--38-33--43 will be required.

Vapor line 32 continues past line 33% and joins line 2l: at the: entrance to the common leg 22' leading to blower 23. A vapor heater III is connested between, the outlet of blower 23` and vapor inlet I9. The heater 4I may be a conventional shell-and-tube type, the vapors passing through tubes heated by any convenient fluid, such as steam. admitted to the shell by means of steam inlet. pipe 43. Condensate leaves at outlet pipe 43a. To. insu-reV the supply of sucient heat to evaporate all but a residual trace of solvent, yet to prevent excessive heating of the particles, a conventional temperature controller 42 controls the admission of steam through l-ine 33 to heater 4I in inverse relation to the temperature. of the particles being discharged through outlet i?.

Vapors condensed incondenser 26 are removed through a liquid pipe 44 for further handling andl recovery of at least the solvent portion thereof. Vessel I 0 is usually unheated although it is usually suitably4 insulated. On the other hand, the domes` and lines in the vapor circuit are usually steamjacketed in conventional manner to prevent loss of heat resulting in dust problemsv and to enable the controls of this system to be utilized without regard to the vagaries of the ambient temperature. Normally, there is less dustv in the desolventizer than there is in the deodorizer owing toL the fact that the net make of vapor comprising evaporated solvent and water vapor isY largely freed. of dust in the desolventizer by contactv with the relatively wetter flakes or particles. Even so, steam jacketing as aforesaid may be desirable because in the presence of even some dust any condensation may cause solid material to accumulate on cooler spots on the uniacketed walls of the vapor passages restricting such passages and causing mechanical difculties.

Deodorizer vessel il is a conventional horizontal cylindrical vessel which receives solid organic particles from vessel It through a rotary vane lock valve 48 and an inlet pipe 49. Within vessel 4l a rotating shaft 50 having paddle arms 5l and helically disposed paddles 52 at the respective ends thereof cause such particles to progress through vessel 4l and pass out through outlet 5S. On the other hand, vessel 4l may -be constructed in a manner similar to the construction of vessel I il. Such particles discharged from deodorizer vessel 5'! are transmitted by a vapor look rotary valve Ell similar to valve 48 into an aerating drum 55.

Gaseous fluid for evaporating the remaining solvent in the particles passing through deodorizer 47 exits from vessel 4l with the evaporated solvent and Water vapor therein through a vapor dome 5l and passes through a vapor line 52 into the bottom of a condenser 63. As illustrated, condenser 63 is a direct contact condenser containing a plurality of conventional mixing baiiles 64 therein. Because the particles are relatively drier in the deodorizer, there is more opportunity for the solvent evaporated therein to entrain some dust. Therefore, the provision of a direct contact condenser 53 will serve both as a scrubber to remove such dust and as a condenser of the predetermined proportion of solvent and water vapor.

Non-condensable gas and such predetermined portion of the solvent vapor and Water vapor, not economical to condense, pass out of the top of the condenser 53 through a vapor line 65 and into the intake of a blower 55 which discharges into vapor line 155. A conventional temperature controller 5'? maintains the stripped gaseous fluid leaving the top of condenser 53 at such low temperature as will provide a negligible loss of solvent in the gas passing out through the rotary valve lock 54.

Condenser 53 uses liquid solvent as the condensing liquid which condensing liquid is introduced at the top of the condenser through inlet 85. All of the liquid material from condenser 53 is discharged through an outlet S9 at the bottom thereof and passes through a line 70 into a conventional separator drum 'Il having a conventional liquid level gauge 'I2 thereon. The pump 5E) removes suiiicient liquid from the bottom of the drum 'Il to withdraw substantially all of the Water and nes and thus prevent the formation of any interface Within the drum which might give rise to troublesome emulsion formations therein. In general, a little solvent will be Withdrawn through the suction line to the pump 90 While solvent Will be Withdrawn through the line 73.

Liquid solvent Withdrawn through outlet 'E3 then passes into a surge tank 15. The net solvent recovered flows through pipe 92. Solvent for condensing vapor in the condenser t3 is circulated from the bottom of tank l5 by recirculating pump 'i6 to a conventional solvent cooler 'Il through a liquid line l5. Solvent cooler 'Il may be a shelland-tube type with the solvent liquid passing through the tubes and With a refrigerant circulated through the shell. Such refrigerant may be supplied by a refrigerating machine through a line 8l, the refrigerant returning to machine 80 through line 82.

The cooled liquid solvent passes out of cooler 'El through liquid line 84 in such volume as permitted by temperature controller 6l. Hence, by these means the eilluent gaseous iiuid leaving condenser 63 through vapor line 55 is substantially at a constant temperature and of a constant composition and substantially at a uniform pressure, to Wit, atmospheric. Deodorizer vessel 4l is not steam jacketed in the usual manner but is usually insulated. Moreover, the gaseous iiuid entering vessel 4l through vapor line 45 and vapor inlet dome is cooled to such extent that the sensible heat of the particles passing through deodorzer vessel il evaporate the remaining liquid solvent in such particles and thereby raise the temperature of the gaseous fluid passing through vessel 4l countercurrent to the passage of the particles therethrough. Despite the composition and temperature changes of such gaseous fluid in passing through vessel 4l, the conditions of operations are such that the saturation temperature of such gaseous uid is not reached at any time within vessel 4l. Usually vapor outlet dome 6| and vapor line 62 will be steam jaclreted to prevent condensation with resulting dust deposition.

Means for recovering solvent condensed in the condenser 26 is generally similar to that previously described for recovering solvent condensed in condenser 63. It consists of a separator drum lla from which liquid solvent overflows through pipe 13a. Water, nes, and some solvent are removed. from the bottom of the separator 'ila by means of pump a. The liquid and solids from the pumps 90 and 30a are discharged into pipe 5| Which conducts them to the feed conveyor Il, inwhich the fines and water are recovered by being incorporated into the body of flakes to be desolventized. This recycle of iines and Water maintains the bulk and moisture content of the particles the same after desolventizing as they were before desolventizing. Solvent recovered from the overow pipes 73a and 92 is combined and delivered by suitable pump, if necessary, to a solvent storage tank not shown in the drawing.

A vapor pipe l5 connects lines 36 with a vapor line 45 in the gaseous luidcircuit of a deodorizer vessel 4l and thereby equalizes the pressure in the gaseous fluid or vapor circuit of said deodorizer vessel lll With the pressure in the vapor circuit of desolventizer vessel Hl. Further, makeup gas, such as carbon dioxide, passes through line t5 to Whatever extent is required to establish the volume of gaseous fluid in the deodorizer vvessel circuit at that required for operation sub stantially at atmospheric pressure.

Aerating drum 55 is provided with a conventional longitudinal shaft and paddles similar to those in vessel 4l for moving the particles discharged from deodorizer vessel 4l toward and out of an aerator outlet 56. A hinged gate 5l freely opens, or a vane lock may be used, to permit the discharge of the flakes through outlet 56. Air is passed through vessel 55 in a countercurrent direction through dome inlet 58 and exits through gas outlet 59 and stack 59a. A fan `Si! supplies the necessary air for aeration purposes. The aeration which occurs in drum 55 is desirable to purge the mass of particles of any residual trace of solvent.

The significance of the new system of this invention may perhaps be best illustrated by reciting pertinentA design infomation for a proposed plant toztreat, extracted soybean flakes from 25 tons of beans using commercial hexane having an average boiling point aboutl 150 F. at 76.0; mm. of mercury absolute. Such a plant might be expected to have a desolventizer vessel with an internal diameter of about 30 and' a deodorizer vessel with. an. internal diameter of about 24". The use of an incombustible gas such as: carbon dioxide may be provided to lower the partial pressure of' the solvent vapor in the evaporating gaseous fluid circuits to keep the saturationy temperatures at' all times below the desired maximum. Suchgaseous fluid, in addition to the solvent and gas therein., hasv a small proportion: of Water vapor in the composition thereof. Thus, and without any limitation of this system thereto, the following tablefurnishes an example of approximate temperature. and flow conditions for such a continuous soybean flake desolventizing operation pursuant to thisinvention:

` Approximate temperature. and' fow conditions for cited example' In the proposed example it mightr be expected that the soybean flakes upon entryA into desolventizer lll mightr haveA hexane therein inV the amount of 50% by weight of the flakes them selves on a moisture-free basis. Upon discharge of such fiakes from the desolventizer, such as vessel i', such liquid' solvent therein might be expected to be reduced to about 2% by weight of the flakes on a moisture-free basis. That 2% of liquid solvent is substantially Wholly evaporated in the deodorizer vessel such as vessel 41.

There is but about a lli-degree rise in temperature of the flakes to be expected in the desolventizer vessel and a AI0-degree drop in the temperature. of the flakes to b e expected in the deodorizer vessel. Thev presence of solvent. in the particles passing through` the desolventiner protects them from attaining temperatures in excess. of the Wetbulb temperature of. the solvent. vapor.

It is apparent that. engineering changes in the arrangement, sizes and proportions ofV the various items of equipment and in the circuit connections and flow conditions of the materials passing through the system for particular desired operations on different types of organic particles may be made without departing` from the: spirit ofthe invention andthe scope of the appended claims..

I claim:

I. In a continuous low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, successively passing solvent-extracted solid organic particles through a desoiventizer vessel and a deodorizer vessel., passing an atmosphere including an incondensable gas' and capable of receiving and retaining solvent vapor from said' solid' orga-nic` particles in sai'dl vessels during said respective passages, separately withdrawing said' atmospheres respectively from said vessels separately, condensing a portion of the solvent vapor from said atmospheres so Withdrawn, recycling the balance` ofthe said' `atmospheres respectively so Withdrawn to said vessels, and supplying said incondensable gas to said atmospheres to maintain generally uniform pressure in said system.

2. In a continuous system for evaporating sol- Vent from solvent-extracted solid organic particles, the steps comprising, charging solvent-extracted solid organic particles to a desolventizer, moving said solid organic particles through said desolventizer, passing a gaseous uid including an inert gas through said desolventizer and in contact with said solid organic particles, heating said gaseous iiuid prior to its entry into said de'- solventizer, controlling the extent of said heating by the temperature of said solid. organic particles adjacent the outlet of said desolventizer, condensing at least a portion of the solvent vapor in the gaseous iiuid leaving said desolventizer, controlling the extent of said condensing' by means of the temperature of said gaseous iluid leaving said desolventizer, recycling the gaseous fluid not so condensed from said condensing, step through said heating step to said desolventizer, and connecting said last-mentioned gaseous fluid before said heating step to a source of said inert gas at a substantially constant pressure.

3. In a continuous system for evaporating, solvent from solvent-extracted solid organic particles, the steps comprising, charging solventextracted solid organic particles to and moving said solid organic particles through a desol'ventizer, moving a plurality of streams of gaseous iiuid including an inert gas through said desolventizer, withdrawing said streams from said desolventizer and returning them thereto through passages. having at `feast one common leg, discharging into said desolventizer, condensing. a predetermined amount of the condensable portion of at least one of the streams so Withdrawn, heating at least part of the gaseous. fluid recycled to said desolventizer, and supplying. inert gas to said system to maintain a generally uniform pressure therein Without any substantial admission of air thereto.

4. In a continuous system for evaporating solvent, from solvent-extracted solid organic particles, the steps comprising, charging solvent-extracted solid organic particles to the desolventizer. through an inlet adjacent one end thereof., moving said solid organic particles through said desolventizer to an outlet adjacent. the other end thereof, introducing a gaseous fluid into said desolventizer intermediate the ends thereof., Withdrawing gaseous fluid so introducedl including evaporated vapors from said solid organic particles from said desolventizer adjacent both ends thereof, controllably condensingV condensable portions of one of said streams of said gaseous duid so withdrawn, reintroducing to said desolventizer the uncondensed portion of said stream subjected to said condensing step reintroducing to said desolventizer the other of said streams so withdrawn and heating said gaseous fluid so reintroduced prior to such reintroduction.

5. In a continuous low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, passing said solid organic particles through a solvent vaporizing stage, introducing a solvent-evaporating atmosphere' into said stage in contact with hun said solid organic particles intermediate the ends of the passage thereof, said atmosphere dividing into two streams respectively countercurrent and cocurrent, regulating the flow of said cocurrent stream to a xed rate, withdrawing said cocurrent stream from said solvent vaporizing stage, withdrawing said countercurrent stream from said solvent vaporizing stage, controllably condensing the vaporized solvent from said countercurrent stream, recycling said cocurrent stream and the remainder of said countercurrent stream to said solvent vaporizing stage, and heating said recycled streams prior to their entry into said solvent Vaporizing stage.

6. In a low-temperature system for evaporate ing solvent from solvent-extracted solid organic particles, the steps comprising, passing said solid organic particles through a solvent vaporizing stage, introducing a solvent evaporating atmosphere into said stage in contact with said solid organic particles intermediate the ends of the passage thereof, dividing said atmosphere into two streams respectively countercurrent and cocurrent, regulating the fiow of one of said streams to a substantially uniform volume, withdrawing said cocurrent stream from said solvent vaporizing stage, withdrawing said countercurrent stream from said solvent vaporizing stage, ccntrolledly condensing the solvent in the other of said streams in an amount substantially equal to the amount vaporized from said particles, recycling said one of said streams and the remainder of said other of said streams to said solvent vaporizing stage, heating said recycled streams prior to their entry into said solvent vaporizing stage, and supplying make-up gas to the atmosphere being so recycled.

7. In a low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, passing said solid organic particles through an initial solvent vaporizing stage and then passing said solid organic particles through a second succeeding solvent vaporizing stage, recirculating a solvent evaporating atmosphere through said initial solvent vaporizing stage, condensing from said atmosphere so recirculated substantially the quantity of solvent evaporated in said initial solvent vaporizing stage, recirculating a like solvent Vapor receiving atmosphere through said second solvent vaporizing stage, condensing solvent vaporized in said second solvent vaporizing stage from the atmosphere so recirculated therethrough, and supplying common make-up gas to said atmospheres so recirculated in advance of the reentry cfsaid atmospheres into said stages.

8. In a low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, passing said solid organic particles through an initial solvent vaporizing stage and then passing said solid organic particles through a second succeeding solvent vaporizing stage, recirculating a solvent vapor receiving atmosphere through said initial solvent vaporizing stage at a generally uniform pressure, condensing from said atmosphere so recirculated substantially` the quantity of solvent vapor received thereby, recirculating a similar solvent vapor receiving atmosphere through said second solvent vaporizing stage at said generally uniform pressure, condensing solvent vaporized in said second solvent Vaporizing stage from the at mosphere so recirculated therethrough, and providing a common supply of make-up gas at said generally uniform pressure for said atmospheres 10 so recirculated rafter the respective condensing treatment thereof.

9. .T n a continuous low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, successively passing solvent-extracted solid organic particles through desolventizer and deodorizer stages, passing an atmosphere including an incondensable gas through each said stage in contact with said solid organic particles at a generally uniform pressure, said atmospheres being unsaturated and at temperatures respectively suiiicient to retain solvent vapor generated from the solvent in said solid organic particles during said respective passages, withdrawing said atmosphere from said respective stages, controlled condensing solvent from said atmospheres so withdrawn, recycling the respective balances of said atmospheres subjected to said condensing to said stages, and maintaining a reservoir of an incondensable gas for pressure control of and as make-up for said balances of said atmospheres before reintroduction into said stages.

10. In a continuous low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, passing said solid organic particles through a solvent vaporizing stage, recirculating a solvent vapor receiving atmosphere through said solvent vapor izing stage at an initial temperature substantially lower than at least the inlet temperature of said solid organic particles, condensing from said solvent vapor receiving atmosphere so recirculated substantially the quantity of solvent vapor received thereby, and refrigerating the remainder of said atmosphere in the course of said condensing prior to the recirculation of said remainder of said atmosphere, whereby sensible heat in said solid organic particles is used in the vaporizing of the solvent therein for retention thereof by said solvent vapor receiving atmosphere.

l1. In a continuous low-temperature system for evaporating solvent from solvent-extracted solid organic particles, the steps comprising, successively passing said solid organic particles through two solvent vaporizing stages, recircu lating a gaseous atmosphere in each o1 said stages, said atmosphere including an incombustible gas, condensing from said respective atmospheres so recirculated substantially the quantity of solvent evaporated during said respective recirculations in said respective stages, heating the remaining atmosphere for recirculation to the rst of said stages, refrigerating the remaining atmosphere respectively for recirculation to the second of said stages,A controlling the respective temperatures of said respective remaining atmospheres by said condensing, and generally equalizing the pressure of said remaining atmospheres.

12. In a continuous system for evaporating solvent from solvent-extracted solid organic particles, apparatus comprising, a solvent vaporizn ing vessel through which said solid organic par ticles are passed between a solids inlet and a solids outlet therein, a gaseous inlet in said desolventizer vessel through which a solvent evaporating atmosphere is continuously introduced and circulated, a gaseous outlet for continuously removing said atmosphere after its passage through said desolventizer vessel, a recirculating passage connecting said gaseous outlet to said .gaseous inlet, a condenser connected in said recirculating passage, a temperature controller connected adjacent the outlet of said condenser and adapted to maintain constant the :temperature of said atmosphere leaving said condenser, a heater connected in said recirculati-ng passage following said condenser, and a temperature controller for the temperature oi said atmosphere being recirculated through said -heater `.controlled by the temperature of said solid organic ,particles leaving said desolventizer vessel.

13. In a continuous system for evaporating solvent from solvent-extracted solid organic particles, apparatus comprising, a solvent vaporizing vessel through which said solid organic particles are passed between a solids inlet and a solids outlet therein, a gaseous inlet in said desolventizer vessel through which a solvent evaporating atmosphere is continuously introduced and circulated, a gaseous outlet for continuously removing said atmosphere after Yits passage through said desolventizer vessel, .a recirculating passage connecting said gaseous outlet to said gaseous inlet,

a `condenser connected in said recirculating passage, a temperature controller connected adjacent the outlet of said condenser and adapted to maintain constant the temperature oi said atmosphere leaving said condenser, a surge reservoir vessel in said recirculating passage adapted to maintain said atmosphere at a substantiallyr uniform pressure, means adjacent said surge vessel for making an inert gas continuously available to said atmosphere as make-up, land a heater connected in said recirculating ypassage between said surge vessel and said gaseous inlet.

14. In a `continuous low-temperature system for evaporating solvent from solvent-extracted solid organic particles, apparatus comprising, a plurality of solvent vaporizing vessels through which said solid organic particles are successively passed between a solids inlet and a solids outlet in each thereof, a gaseous inlet and `a gaseous outlet in each of said vessels through which a solvent vapor retaining atmosphere including an inert gas is continuously passed, a recirculating passage between each 4of such gaseous inlets and said gaseous outlets on each vessel, a .duct connecting said recirculating passages to equalize the pressure therebetween, a condenser yconnected in each of said recirculating passages, means for maintaining the temperature of the non-condensed portion of said atmospheres passing through said recirculating passages at respectively predetermined temperatures, means for maintaining said atmospheres at a substantially uniform pressure and `for supplying fresh quantities oi said inert gas as make-up, and a heater connected at least in the recirculating passage for said rst-mentioned vessel between the condenser in such recirculating passage and the respective gaseous inlet for such vessel.

15. In a continuous system for eva-porating solvent from solvent-extracted solid organic particles, apparatus comprising, a desolventizer vessel through which said solid organic particles are passed, a gaseous inlet intermediate the ends of said desolventizer vessel through which a solvent evaporating atmosphere is continuously introduced, gaseous outlets adjacent the ends of said desolventizer vessel for continuously removing said atmosphere after its Vpassage through said desolventizer vessel, a passage Iconnecting each said outlet to said inlet to afford recirculation of said atmosphere, a condenser connected in one of said passages to condense substantially that quantity of solvent evaporated by said atmosphere, an oriice connected in the other of 12 said passages to proportion the volume of said atmosphere passing through said respective passages, and diierential temperature producing means connected to at least one yof said passages and communicating with the vapor outlet of said condenser.

16. In a continuous system for Yevaporating solvent from solvent-extracted solid organic particles, apparatus comp-rising, .a desolventizer vessel through which said solid organic particles are passed, a gaseous inlet intermediate the ends of said ldesolventizer vessel through which a .solvent evaporating atmosphere is continuously introduced, gaseous outlets adjacent the ends of said desolventizer vessel for continuously removing said atmosphere after its passage through said desolventizer vessel, passages connecting said outlets to said inlet to aiord recirculation of said atmosphere, a condenser connected inone `or said passages for said atmosphere to condense substantially that quantity of solvent vaporized 'by said atmosphere, an orifice connected in the other of said passages for said atmosphere, and a heater positioned in said one of said passages between said condenser and said inlet.

17. In a low-temperature system for evaporating solvent from solvent-extracted solid organic particles, apparatus comprising, a plurality voi solvent vaporizing vessels through which said solid organic particles are successively passed between a solids inlet and a solids outlet in each thereof, a gaseous inlet and a gaseous outlet in each of said vessels through which a solvent evaporating atmosphere including an inert ,gas is continuously passed, a recirculating `passage .between each of said gaseous inlets and said gaseous outlets respectively, a duct connecting said recirculating passages to equalize the pressure :therebetween, a condenser connected in Veach of said recirculating passages, means `for maintaining the temperature of the uncondensed portion of 4said atmospheres passing through said recirculating passages at respectively predetermined temperatures for Vsaid respective vessels, means for supplying make-up quantities fof said gas to said recirculating passages, a heater connected in said recirculating passage for the iirst lof said vessels between said condenser therein and said Vgaseous inlet respectively, and means for refrigerating the atmosphere passing through the said recirculating passage of the second or said vessels.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 705,787 Pratt July 29, 1902 1,143,623 Grosvenor June 22, 1915 1,277,895 Foster Sept. 3, 1918 1,371,914 Lewis et al Mar. 15, 1921 1,515,596 Harris Nov. 18, 1924 1,676,786 Lissauer July 10, 1928 1,820,986 Peebles Sept. 1, 1931 1,863,803 Panten'burg June 21, 1932 1,988,678 Arnold Jan. 22, 1935 `2,060,389 Wigelsworth Nov. 10, 1936 2,064,084 Sannio Dec. 15, 1936 2,152,665 Rosenthal Apr. 4, 1939 `2,198,412 McDonald Apr. 23, 1940 2,491,060 Robinson Dec. 13, 1949 2,571,143 Leslie Oct. 16, 1951 FOREIGN PATENTS Number Country Date 211,599 Great Britain Feb. 28, 1924 407,526 Great Britain Mar. 22, 1934 

1. IN A CONTINUOUS LOW-TEMPERATURE SYSTEM FOR EVAPORATING SOLVENT FROM SOLVENT-EXTRACTED SOLID ORGANIC PARTICLES, THE STEPS COMPRISING, SUCCESSIVELY PASSING SOLVENT-EXTRACTED SOLID ORGANIC PARTICLES THROUGH A DESOLVENTIZER VESSEL AND A DEODORIZER VESSEL, PASSING AN ATMOSPHERE INCLUDING AN INCONDENSABLE GAN AND CAPABLE OF RECEIVING AND RETAINING SOLVEN VAPOR FROM SAID SOLID ORGANIC PARTICLES IN SAID VESSELS DURING SAID RESPECTIVE PASSAGES, SEPARATELY WITHDRAWING SAID ATMOSPHERES RESPECTIVELY FROM SAID VESSELS SEPARATELY, CONDENSING A PORTION OF THE SOLVENT VAPOR FROM SAID ATMOSPHERES SO WITHDRAWN, RECYCLING THE BALANCE OF SAID ATMOSPHERES RESPECTIVELY 